Page 551 - Elements of Chemical Reaction Engineering Ebook

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Chap. 8, Questions and Problems 52
(a) The reaction discussed in Problem P8-15 is to be carried wdt in a single
plug-flow reactor immersed in a coolant and in a radial flow reactor
immersed in the same coolant. The tubular flow reactor is 2 ft in diameter.
The height of the radial flow reactor is in. and the diameter of the inilet is
1 in. In both cases the coolant temperature is 100°C and the werall
heat-transfer coefficient is 2000 J/ m2 * h + "C . Plot conversion and ternper-
atures as a function of reactor radius.
PS-19, The zero-order exothermic liquid-phase reaction
A-+B
is carried out at 85°C in a jacketed 0.2-m3 CSTR. The coolant temperature in
the rcacitor is 32°F. The heat transfer coefficient is 120 W/ m2 K . Determine
the critilcal value of the heat-transfer area below which the reactor will run
away and explode [Chem. Eng., 91(10), 54.(1984)].
Additional information:
k = 1.127 kmol/m3.min at4O"C
k = 1.421 kmol/m3.min at 50°C
The heat capacity of the solution is 4 J/g. The solution density is 0.90 kgi'dm3.
The heat of reaction is ;SO0 J/g. The feed temperature is 40°C and the feed
rate is 90 kg/min. MW of A = 90 g/mol.
PS-20B The elementary reversible liquid-phase reaction
A-B
takes place in a CSTR with a heat exchanger. Pure A enters the reactor.
(a) Derive an expression (or set of expressions) to calculate G(T) as a fuilc-
tion of heat of reaction, equilibrium constant, temperature, and so on.
Show a sample calculation for G(T) at T = 400 K.
(b) What are the steady-state temperatures? (Am.: 310, 377,418 K)
(c) Which steady states are locally stable?
(a) What is the conversion corresponding to the upper steady state?
(e) Vary the ambient temperature T, and make SI plot of the reactor temperature
as a function of T, , identifying the ignition and extinction temperatures.
(f') If the heat exchanger in the reactor suddenly fails (Le., UA = 0), what
would be the conversion and the reactor temperature wher. the new upper
steady state is reached? (Ans.: 431 K)
(g) Write a question that requires critical thinking and then explain why your
question requires critical thinking. [Hint: See Preface p.xx]
(h) What is the adiabatic blowout flow rate, u,, .
(i) Suppose that you want to operate at the lower steady state. What parameter
values would you suggest to prevent runaway?
Additional information:
UA = 3600 cal/min. K EIR = 20,000 K
Cp, = Cp, = 40 cal/mol* K v- 10dm3
A HRx = - 80,000 cal/mol A uo = 1 dm3/min
Keq = 100 at 400 K FAo == 10 mol/min
k = 1 min-' at 400 K
Ambient temperature, T, = 37°C Feed temperature, To = 37°C